Date: Thu, 30 Mar 2000 09:15:54 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: Bruce Evans <bde@zeta.org.au>, Mike Smith <msmith@FreeBSD.ORG>, freebsd-current@FreeBSD.ORG Subject: Re: SMP buildworld times / performance tests Message-ID: <200003301715.JAA73702@apollo.backplane.com> References: <1274.954416252@critter.freebsd.dk>
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:In message <Pine.BSF.4.21.0003302111410.3247-100000@alphplex.bde.org>, Bruce Ev
:ans writes:
:>On Wed, 29 Mar 2000, Mike Smith wrote:
:>
:>> Just following on from this, one thing that I can see immediately being
:>> very important to me at least is a spinlock in the timecounter structure.
:>> Calcru and various other things call microtime(), and we're going to want
:>> to lock out updates and parallel accesses to the timecounter. What
:>> should we be using for an interrupt-disabling spinlock?
:>
:>Nothing. Accesses to the timecounter struct are already MP safe and fast.
:>Only the i8254 timecounter hardware currently needs interrupt-disabling,
:>but it is hopefully never used on SMP machines.
:
:Worse. It is used by default on SMP machines which don't sport the
:PIIX timecounter.
:
:--
:Poul-Henning Kamp FreeBSD coreteam member
:phk@FreeBSD.ORG "Real hackers run -current on their laptop."
:FreeBSD -- It will take a long time before progress goes too far!
The general problem with the timecounter is that not only is the hardware
indeterminant, but the timecounter structure itself is *NOT* MP safe,
at least not by my read of it.
It also doesn't appear to be interrupt safe. If a microtime() or
getmicrotime() call is interrupted and the interrupting interrupt calls
microtime(), it can corrupt the data returned by the first guy and
even corrupt the structure.
-Matt
Matthew Dillon
<dillon@backplane.com>
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